hamilton



H. s. HAMILTON v APPARATUS AND METHOD FOR MEASURING TRANSMISSION Filed Dec. 5.,

INVENTOR fl Jfiami/Zw/a ATTORNEY retested Sept; 25; 1923 o. 7

ArrARAT s en i'ifianincn ri-ssio lm ma aw fileki ame 1 92 1 "Tau ll whom it ii apjconoerna' residing New York in the'county o'f Bronx and State of NeW York',''haVe in} i entsin Apparatus vented @erminimpmve 7 I 7 and Methods for Meas firing Tralisni 'sslon,

of which the following is a specification.

Tia

"u The; principal object -of my invention is: to provid'efa new and appropriate apparatus transnii ssion' efiicienoy of i a piece of appa j ratu's at particular; frequencies fofiw'hich I such measurements n ay' he other-object of'my ini' entioniis suitably to p'r ovide that in making sufoh measurements 1 there shall {he protection from'lialse- .efi'ectjs 3 that might ,be occasioned .th e'introduc V These and other objects of 'm'y invention;

tion of currents, of extraneous] frequencies.

Will hecolnef apparent on considerationf'of alimited numherof specific examples which I Will now describe to. illustrate the principle of the invention:

7 stood thatthe definition of the, invention Willihe givenin'the appended claims andf that the following description will apply specifically to these illustrative examples I given thereunder, 5 v l Referring ltothe drawings, Figure 1 is j general diagram of-app'ara'tus for ineaSur i ing] the transmission efficienoy "oiffa. geographically eXtended'line;FigiQ adetail diagram of an'adjustable network forming part of this systemg Figfl-i is adiagrain sho-win t'ransmis'sion a's'a function of ire-1 quency,flwhi.ch Will he referred to'hinathe course of this specification, and Fig.4 is diagram illustrating the application nof my invention in connection with the measureinentof the efiioiency of a repeater; 1

Referring tofFig. l, the geographically 'extendedqline L oonneotsthe distant, office A with thehome officegB and it'is desired to measure-its transmission equivalent. The

equivalent referred to depends upontheate tenuation of. the current in; the line and the gain of "any amplifying apparatus It is: commonly ,measured in standard', milesy A standard mileis .a nile lengthof cable pair. of certain dimensions; and: constants, "which are Well known, and a loss orkattenuation ofia certain number of standardf-- f miles is theloss or attenuation that would be'produced on a circuit oft-that numberof miles of-such cable air. Similarly a gain.

generators of the salne frequency Whose ou put mayivbe 'controlledjby 'the adjustableire v sistances 2 and 2; I The'ineasuringfinstru- Ine1 1ts'i5 and i5' are alike. f The 'iinpeda ilcei usefulmethod and} for" measuring the elsii ed. @An-i.

[It will be under- '2; are ad usted (to ioperationfof thefapparatus,

tothe impedance of theline-L. Current duee jrmnolnn s..m nmeimpmwAssam, ;;.iri ,,ggsrem TOQAMERiCAN uinLnPHoNE l 1 AND EG AP omen/any,

JLICORKPGBATYIGNI EWZYQRK,

the effect produced by V 'I and 1- are:similarjalteriiating o rrent of the device 4 is very glow compared, to theiqninipedanoe of th ejfcircuit com-j" p ri'si'ngf' "th elenients] 7 andfithei "line u'nde .iftes't', gso tha't"a Very large'ffifrac p The fpotential across the terminals of Zir= sistance 4 is flthereffore,practically. inde ,ancethe same looking in and out oifjthe line L at the respectivefofiices; and this is done in such al'way' as to 'make resistances I 4; and 14-; equal, Then'the resistances 2' and Q I ake the instruments Q W en-awe switch 91g maeyieo'sim: show I in full lines :a certain eurrenh due acertain electromoti ze', force, i receiyedf structural features shown in Fig. llwillghe apparent from; the diagram. or" vx vill'f be ex p].ained in ;the following"description of the l/Viti theiswitehes in the positionsfshoiieiand 7" and the secondary 'ofthe transformerf 8 arefadju'sted to correspond approximately to 'the generator lflthefn flows throughthe i oalibr atingline 12, amplifier 16; filter 17-,lan-

ratusgisi proportional to ith e reading of "thefl current, of any coni enient arbitrary value 1 I f theijseooiifdary "ourrentfoff m n formerfi floWs through the resistanceji, J 70' l in full linesin thedra ving the'fi sistances Q I 00 A 7 other amplifier. 18, gaiiotheri -amplifier and! I currentl li nitingidevice 19,-,rectifier; 'ineasuring; instrument 21.? The: potential V impressed at thesending end of theapp'ameter55and'the'currenttra-nsinitteclis-indi i and thepotentiometerlS is adjusted until the pointer of meter 21 standsat a prede terlnined position, the middle oit the scale. I

from the distant. oflice A. comes over the line L to theswitch 9, then through thenet-worh 13, and the rest of the way as before to the meter 21. The resistance 1 is made equal to resistance 4;, and resistance 2 is adjusted "filter 17 connected as just explained,

land 1'.

until the reading; of faster Yis the same as thep-revious reading of meter 5; thus it is known thatthe voltage imuressed on the line; at the distant ofiice A is the same as was thevoltae e impressedon the measuring an;

paratus at the hon e 'ofiice B for calibration The adjustable measuring line 13 is c'o.n-'

structed tofhave the same transmission equ valent as the cahl at ng the associated Chill indicates; CG1Q;'il lZ.if is,

when the. rotatable contactor 15 is thrown 'to the opposite extreme from that indicated 4 'in Fig. 1,'the transmission equivalent for the line 13 will be the same as for the line The calibration for the device 13eisin standard miles and giues the number of miles that are jcut' out from the line 13 the adjust-r Inent is niade toward that shown in the figurd The impedance oi the 'line, 13 is. constant at all ad ustments and the same as forthe line 12.. I 7 It is assumed that when the switches 9, 11

14 were thrown the contactor 13 was at the position which made the transmission loss the saine for the line 13 as for the lincf 12. Accordinglyn the throw the switches merely changed conditions by the lntl'OdUO tion oi the line L; this caused ascertain,

transmission loss so that less current than before got through to the so as gradually toreduce the attenuation loss in the line until the reading; of .the

instrument 21. is restored to the value it had before the switches 9 11 and 1 1- werethrown.

This means that the loss in line Lis compensated by reduction of loss in the line 1 3 and* this loss is read ofi directly instandard miles that cooperates with the rotaton the scale 111,9, contactor 13.

The filter l'i is alng'h pass filter which will have its critical orcut-otl frequency at a point somewhere within th lower part of the essential voice frequency rang: I say at about 500 cycles per second. Most intert'ering frequencies are lower than this, so that any such lowerffrequencies will he shunteil 1out by t;e filter 17 andwill not aii e'ct the reading of the instrument '21. TVith the course only frequencies above its critical. queney can be employed at "the generators The receiving apparatus having thus been calibrated, switches 9, 11 and 14 are thrown. to their dotted line positions so that current line 12 when measuring instru nent 21. The contractor 13 is now rotated F or. certain purposes it may become desirable to measure the transmission efliciency of the line L at frequencies below purpose ofthe" condenser 33 is to prevent the formation of circuit to the right through which, continuous current mightj fio w from the plate battery for the audion amplifier 16.

in Fig. 2. It consists of an inductance coil 3-41 and a series ofcondensers 35 and 35.? or which 35 is permanently connected in parallel and'the others .niay he connected likewise by means of the switches 36 /Vith" all the switches .36 open, the cornbination' 34-35 is. resonant at a frequency 01 400. Closing the first switch 36 makes thefentire .conibinationiresonant at 300 Closing, in addition, the. second switch 36 iThe filter 3 l+35 is shown more in detail 7 det "mines the resonant frequency at 200,

"and so on, as indicated by the legends at the-lower part of Fig. 2. The diagram in Fig. 3 shows the gain (or loss) produced by introducing the filter 341%35, as a function of frequency for each ol the 'five -a'cljustinents of the filter. of Fig. 2. t Wlll be seen that the filter is very sharply selective.

At the precise indicated frequency for each adjustnient there is a'certain transmission whichjfalls ofi' rapidly as the frequency deviates on either'side' Accordingly,jit is important that the generators 1 and 1" shall operate accurately at whichever of the lire i r'equencies the. switches 36 set in F 1g; 2. i

i n'estln flor tie transmission a an 'oneo't. these frequencies, if an extraneous interfering frequency gets on the line L, it will be practically elhninatedat the filter 3 1+35, unless it happens to be almost" exactly the same frequency as the one for whlclrthe test- 13 being made. TlllS'COlltingency can beguarded against in several ways, one ofwhich is to notice whether any current'is received 'over the line L, when the circuit of the at 2 in Frau. 1.

generator 1 isopened as lit) 7.

Interfering frequencies are mostly in the range below 500 cycles per second, and hence 1 a mere high. pass'wave filter like 17 is safe 'ficien't for' tests above that frequency, but

when one is making tests below that fre- .quency, he is operating in a "range such that interference be encountered at fr'equencles elther abore or below the test frequench and therefore, 1 ilter. or the are indicatedby I it Will 1165" he *sniael "but filter such as with narrow sharp send the Ilngl selectivity i ore at repeater stationsyth. 1 rent hasqbeen 'shuntedaround' the repeaters; 10

will be 'advantageous,"aspointed On'long is common. to transmit ringing current ata frequency of 135 cycles pers and ma e I to actuate selective-relays? Buti-t:

is becoming the practice to some extent to.

peaters';and Iis'i's one reason Why'it may be. desirable to test the transmission 8fiici'ency of a line, including itsrepeaters at. a frequency below 500 cycles pers'econd, and

uiuthis case particularly at 135 cycles per second; H 1

' In alternating curr ent telegraph';W ork, the "transmission of low frequencies within the range indicated by the legends on.

2 becomes a matter of interest the deg L termination, of the transmission at these frequencies can 'i be Inadexhy'means of. my

invention, involving the use of the filter In Fig.4.} have illustrated the use of;

narrowly-selective filter in o'onnecti'on' withr apparatus 01 testing repeater "gain. The

generator 40 sends out current O f deS1I-Bdfrequency through; a network 41, having-a potentiometer adjustment, to the! primary .12 of a transformer having a divided sec ondaryii- The circuit of one pa r of condnctors 45 goes from the; secondary 4C3 throiigh an appropriate network to the input side of the repeater 4:8 whoseoutput de connected through'the netw kg g w ,the'sWitch' 51.

The circuit ofithe other pair of conductors 4:6 fron'i the transformer secondaryitg goes also to the switchhi; Across the conductors 4-5 is an adjustable resistance 4% and across the conductors 46 is a similar adjustable resistancefil). Both thesejadjustahle resistances and 50 are calibrated 'inysta'ndard miles- The switch 51 connectstwo'circuits' from the" respective conductor pairs @Sfanoly a6 alternatively With the measuring instrument 53 and the resistance 52. The resist-' .zlnce 52 'is made equal to the resistancje' of i the measuring instrument 53.- The networks l7 and 49. are provided in orderto equalize. ,the impedance for var ous repeaters 48 that .VVhen it is desired generator 40 should troduced as shown. next to the" generator.

in Fig. 3: This will shuntout the harl monies so that there Wlll be; transmitted to;

telephone transmission lines) it g current right ithr ough the 7 out harmonics; It; av

e transformer iig current and 50; Whose readings are added,

I the 7' result is attained that {the instrument 53 1e, calibrated resist reads the r-waecm inatterfWhichWay the] switch 5lf=isfthrowni This'means' that the V due to the rep'eaterT' i S is. balanced-by Q losskat/M in addition to the loss at giQ -so that'the" gain can ne read-f ofiifro'm'the call-- and 50 as already described brationsat" 4:4:- claim:

1. Incoinhination, apparatus Whose'trans mission efiici'ency; is to be ineasured at a particular frequency helowifthe essential v volceffrequency range, a source-10f current} atthat frequency applied to such ap Jaratus' atone .e ndhan indicator tolshow the magnitude .ofthe transmitted 'current and thus to 'indicateithe transmission f-efiici'ency, and means to shunt out fromsa 'cl indicator-subs'tantially llficurrents of frequency different from that of said source? r 12. The; method of measuring g I I the trans, V missione'iii'ciency of apparatus ata particular frequency below the eSsentialQvoice ire quency rang.e,' Which consists in applying current of that frequency to one end of such apparatusandmeasuring the'current transinittedto the; other end thereof, and shunting out "an fortuitous"currentsflof other frequencies than the particular frequency for i which it is desired to make the measurement.

.3JApparatu's for measuringthe trans mission efficiency of'a line comprising like .alternatmgcurrent send ng apparatus at the f distantendlof the line and atithe home-end thereof-Q adjustable means at. the home. end

to compensatethe lossin'shifting from the home sendi and means toshunt out iromjthat indicator apparatus to'thedistant send- 1g apparatus, an'indi'cator .at the home end,

all currents'dijfi'ering in frequency from the fundamental frequency off the alternating current apparatus .at thetwo, ends of the line; said app aratusgat the two ends of the lmehavmg ai fundamental.frequency bee A low the essential voice-frequency range. I

4. The-methodof measuring the. transmission efficiency of line ,at'aparticular' requency below the essential-voice frequency j mn' which consists in applyingto anindi,

cator alternatively current generated like generators atthe home end Jof flthe line and the distant end ohservi'ngthe equiv'a lent network Whose lossco'mpensates for. the,

lossfdue to the interposed line "applying the currentsfin Ihoth cases"'to 1 an indicator, and

shunting out from that indicator, cur-rents of ll equencies V I v desired to, make the test; 1

5. In c.ornbinat ion, apparatus Whose'transmission efliciencyis tobe measured at a particular frequency-below the essential voice I frequency range a sourceof current at that frequency applied to such apparatus-at one end, an indicator to show'the magnitude of transmitted current and thus to indicate the (transmission efficiency, and a shunt pared lel resonant to the frequency at wh ch the test is made-whereby currents of other frequency are shunted out and only currents of that particular frequency areitransinitted'to; i it) the indicator:

' '6. In combination, apparatus Whose trans niission; efiiciency is to be measured Lt- 3L particular frequency, a souroe'ofcurrent et to said indicator, whereby currents of other frequencies than that to Which the coi1condenser comblnatlon 1 s parallel-resonant are shunted with respect to saidindicatolif i In'testimony"whereof, I have signed my i ethat freq uency applied to such apparatus at V nameft-o this specification this'2nd1day of December, 1921-. v 7

- i HAROLD S. HAMILTONJ 

